Immunoassays have been used in recent years to detect the presence of infectious diseases. In order for the assay to be useful, it must detect a particular organism with a high degree of reliability. In most cases, this requires the isolation and reaction of antigens peculiar to the organism with corresponding antibodies. For the test to be commercially successful, it also needs to be relatively inexpensive, simple to use and rapid.
One such organism which can be detected by immunoassay is Chlamydia trachomatis (herein C. trachomatis) which is one of two microbial species of the genus Chlamydiaceae, order Chlamydiales. There are 15 or more strains of this species which are the causes of a number of human ocular and genital diseases including trachoma, inclusion conjunctivitis, lymphogranuloma venereum, nongonococcal urethritis and proctitis. Infection from C. trachomatis is pervasive in the general population so that it is believed that there are millions of cases each year of nongonococcal urethritis alone.
Gonorrhea is a disease usually transmitted by sexual contact caused by a bacterium of the Neisseria genus, especially N. gonorrhoeae. The disease has plagued mankind for thousands of years, and although antibiotics have helped control its spread, it still persists in epidemic proportions in many parts of the world. The importance of detection and treatment of this organism is well recognized. N. meningitidis and N. lactamica are also species of considerable medical and diagnostic interest.
Because of the widespread nature of these diseases, there is considerable interest in having a rapid, simple and reliable test for detection of chlamydial and gonococcal organisms. Considerable research has been carried out to find useful ways to extract detectable antigen from chlamydial organisms. See for example, U.S. Pat. Nos. 4,427,782 (issued Jan. 24, 1984 to Caldwell et al) and 4,663,291 (issued May 5, 1987 to Rose) and E. P. Publications 174,106 (Becton) and 193,431 (Caldwell et al).
Assays for C. trachomatis and N. gonorrhoeae carried out using a solid support are described in U.S. Pat. Nos. 4,497,899 and 4,497,900, respectively (both issued Feb. 5, 1985 to Armstrong et al and Abram et al, respectively). The described assays are performed by extracting antigen from the organism and coating it on a bare solid support. The coated antigen is then detected with either one or two antibodies, one of which is suitably labeled. The critical feature of the assays appears to be the use of a solid support for attachment which is untreated or uncoated with material. Attachment of antigen is apparently achieved by incubating the coated support for an extended time sufficient to cause adsorption of antigen thereon (Col. 2, lines 51-55 of U.S. Pat. No. 4,497,899). The entire assay described in U.S. Pat. No. 4,497,899 takes at least 3 hours to perform. A similar but somewhat quicker assay is described in U.S. Pat. No. 4,497,900 for N. gonorrhoeae (see Cols. 4 and 5).
In the practice of these known assays, bound antigen and bound immunological complexes are washed with water or a buffer. Caldwell et al [J. Clin. Microbiol., 18(3), pp. 539-545, 1983] describe an immunoassay for C. trachomatis in which wash steps were carried out using a phosphate buffered saline solution containing a nonionic surfactant, Tween.TM. 20. A similar assay for N. gonorrhoeae antibodies is described in U.S. Pat. No. 4,241,045 (issued Dec. 23, 1980 to Gaafar).
Use of known washing procedures in assays for chlamydial or gonococcal organisms is unacceptable because the background is too high or the sensitivity is too low and antibodies are found to bind to the solid supports rather than to antigen.